Add Store+Sync to reading list.

ios/chrome/browser/reading_list/reading_list_pref_names.cc

Index: ios/chrome/browser/reading_list/reading_list_pref_names.cc
diff --git a/ios/chrome/browser/reading_list/reading_list_pref_names.cc b/ios/chrome/browser/reading_list/reading_list_pref_names.cc
new file mode 100644
index 0000000000000000000000000000000000000000..61f06b17c87a69ac6ea43a17c895e7a49d58c545
--- /dev/null
+++ b/ios/chrome/browser/reading_list/reading_list_pref_names.cc
@@ -0,0 +1,15 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ios/chrome/browser/reading_list/reading_list_pref_names.h"
+
+namespace reading_list {
+namespace prefs {
+
+// Boolean to track if some reading list entries have never been seen on this
+// device. Not synced.
+const char kReadingListHasUnseenEntries[] = "reading_list.has_unseen_entries";
+
+}  // namespace prefs
+}  // namespace reading_list